I've found the controls to turn on the power and checked out the four control units on the platform inside the control room. I went outside and turned left, then climbed the steps all the way to the end and there is no telescope anywhere along the way. (I've checked at least four times.)
At the end of this path the way is blocked by a thick, vine-like plant (I assume it's a plant).
I could use the codes from the walk-through, but I'd at least like a chance to find them myself.

Hint: Not a vine-like plant; it's observatory control ropes. Did you notice one control station was kaput?